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The kinetics and mechanism of IrIII-catalysed oxidation of dioxane by CeIV in both aqueous H2SO4 and HClO4 media have been studied at different temperatures under the conditions: [dioxane]T [CeIV]T [Ir]T (ca. 10–6–10–8moldm–3). In aqueous HClO4 media a slow uncatalysed path exists alongside the catalysed path, while in aqueous H2SO4 media the catalysed path is the only kinetically detectable path. In both media, the overall process shows a first-order dependence on [CeIV]T; the catalytic path is first order in [Ir]T and exhibits a non-linear dependence on [dioxane]T. The catalysed path probably involves a pre-equilibrium interaction between the catalyst and substrate leading to an outer-sphere complex followed by the electron transfer in the rate-determining step involving CeIV and an outer-sphere complex formed in pre-equilibrium steps. The catalytic path presumably involves the IrIII/IrIV cycle. In HClO4 media the catalytic efficiency is greater than in H2SO4 media. Activation parameters for different paths have been determined in order to rationalise the mechanistic steps. 相似文献
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Justė Baranauskaitė Valdas Jakštas Liudas Ivanauskas Dalia M. Kopustinskienė Gailutė Drakšienė Ruta Masteikova 《Natural product research》2016,30(6):672-674
The aim of our study was to increase the extraction efficiency of carvacrol, rosmarinic, oleanolic and ursolic acid from the different species of oregano herbs (Origanum onites L., Origanum vulgare spp. hirtum and Origanum vulgare L.). Various extraction methods (ultrasound-assisted, heat-reflux, continuous stirring, maceration, percolation) and extraction conditions (different solvent, material:solvent ratio, extraction temperature, extraction time) were used, and the active substances were determined by HPLC. The lowest content of carvacrol, rosmarinic, oleanolic and ursolic acid was obtained by percolation. During heat-reflux extraction, the content of active substances depended on the solvent used: ethanol/non-aqueous solvent (glycerol or propylene glycol) mixture was more effective compared with ethanol alone. The results showed that for each species of oregano the most optimal extraction method should be selected to maximize the content of biologically active substances in the extracts. 相似文献
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Dalia Nayak Devdeep Mukherjee Aparna Banerjee Jhumpa Mukherjee 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(2):477-480
The present work discusses the complexation behavior of bioligand cysteine with cobalt and the immobilization of this complex
(Co–Cys) onto a biocompatible ligand and common drug base, polyvinylpyrrolidone (PVP). The complexation behavior has been
studied by radiometric method and UV–Vis spectrophotometry. The radiometric method involves dialysis of 60Co–Cys–PVP complex against triple distilled water which subsequently gives the dynamic dissociation constant (k
d) of the complex. The half life of 60Co–Cys–PVP complex calculated from k
d value is 22.6 h against triple distilled water at pH 8.5. The UV–Vis spectra analysis confirms the complexation of Co with
cysteine at this pH and also indicates that the cysteine ligated Co(II) centers easily get oxidised to Co(III) centers (low
spin, d6) in the presence of air at alkaline pH showing no d–d transitions. 相似文献
37.
Gut D Rudi A Kopilov J Goldberg I Kol M 《Journal of the American Chemical Society》2002,124(19):5449-5456
Five octahedral eilatin complexes of the type [M(L-L)(2)(eilatin)](2+) (M = Ru, Os; L-L = bipyridyl-type ligands) were synthesized, and their dimerization via pi-pi stacking was studied by crystallography and (1)H NMR techniques. The X-ray structures of these racemic complexes were solved and revealed that the eilatin complexes are organized as discrete dimers in which the eilatin residues of each complex are stacked in centrosymmetric packing. Chemical shift dependence on concentration in the (1)H NMR spectra support fast dimer-monomer equilibrium, and the structures of the dimers in acetonitrile solution are proposed to be analogous to their solid-state structures. Dimerization constants in acetonitrile were measured for the five racemic eilatin complexes that exhibit different structural parameters, as well as for the two enantiomeric forms of one of these complexes. They were found to be independent of the metal (Ru vs Os), strongly dependent on the steric effects introduced by the L-L ligands (2,2'-bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, and 2,2'-biquinoline), and dependent on the optical purity of the complexes. A clear preference for heterochiral over homochiral dimer formation was demonstrated. This is the first report of chiral recognition in solution, exhibited by simple chemical systems held solely by pi-stacking interactions. 相似文献
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Amr El‐Hag Ali Hassan A. Abd El‐Rehim H. Kamal Dalia El‐Sayed A. Hegazy 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):628-634
A unique natural polymer based colon specific drug carrier was prepared from carboxymethyl cellulose (CMC) and acrylic acid (AAc) in aqueous solution employing γ‐radiation induced copolymerization and crosslinking. The effect of preparation conditions such as the natural polymer content and irradiation dose on gelation process was investigated. The swelling behavior of the prepared hydrogels was characterized by investigating the time and pH dependent swelling of the (CMC/AAc) hydrogels of different CMC content. The effects of the hydrogel composition and pH of the swelling medium on the swelling indices were estimated. The results show that the increment in the CMC content in the feed solution enhances the gelation process. The results also show the dependence of the swelling indices on both hydrogel composition and pH value of the swelling medium. To evaluate the ability of the prepared hydrogel to be used as a colon‐specific drug carrier, the release profile of theophylline was studied as a function of time at pH 1 and pH 7. 相似文献
40.
Valencia Dalia Lillo Rosa E. Romo Juan 《Advances in Data Analysis and Classification》2019,13(4):1083-1103
Measuring dependence is a very important tool to analyze pairs of functional data. The coefficients currently available to quantify association between two sets of curves show a non robust behavior under the presence of outliers. We propose a new robust numerical measure of association for bivariate functional data. We extend in this paper Kendall coefficient for finite dimensional observations to the functional setting. We also study its statistical properties. An extensive simulation study shows the good behavior of this new measure for different types of functional data. Moreover, we apply it to establish association for real data, including microarrays time series in genetics.
相似文献